1. Field of the Invention
The present invention generally relates to devices for interconnecting optical fibers, such as are used in telecommunications, and more particularly to an actuation cap for a fiber optic connector which also facilitates cleaving of the optical fiber.
2. Description of the Prior Art
Optical fibers have become the preferred medium for telecommunications but, as with copper wire, it is still necessary to interconnect optical fibers, for example, during installation or repair, or for connecting them to active optical devices. The present invention is directed to a tool for such a fiber optic connector. In this regard, a fiber optic "connector" often refers to a device which allows repeatable engagement and disengagement of the cable, while a "splice" typically refers to a device which is used for the permanent attachment of two cable ends. These terms should not, however, be construed in a limiting sense as used herein since the present invention is applicable to the installation of all classes of fiber optic interconnection devices.
The prior art includes ferrule-type fiber optic connectors having a cylindrical member (the ferrule) usually made of a ceramic material, zirconia, or alumina, with a central bore for receiving the fiber. The ferrule is held by a collar or backbone which in turn may be surrounded by one of many different coupling shells. For example, a coupling shell having a bayonet-style latching mechanism is commonly referred to as an "ST" connector. An alternative shell having ramped surfaces which latch onto lever arms of a receptacle is known as an "SC" connector. Yet another shell having a simple threaded nut is known as an "FC" connector. There are many conventional techniques for securing an optical fiber in ferrule connectors. See the discussion concerning prior art in U.S. patent application Ser. No. 08/149,641 now U.S. Pat. No. 5,414,790.
The '641 application teaches the use of a combined actuation tool and dust cap which precisely positions the fiber end face with respect to the ferrule end face, more specifically, with the fiber end face extending slightly outward from the ferrule end face. This positioning of the ferrule and fiber is very useful in "cleave and crimp" operations wherein the fiber is cleaved prior to insertion into the connector, and then the cable jacket or strengthening strands are secured to the connector body, with very little, if any, final polishing of the fiber tip. The 641' tool/cap, which is probably the closest prior art, is shown in FIG. 1, as attached to a CRIMPLOK fiber optic connector, designed for field installation of the fiber (CRIMPLOK is a trademark of Minnesota Mining and Manufacturing Co., assignee of the present invention). The depicted connector uses bayonet-style latching with a lug 1 formed on the ferrule collar 2. The ferrule 3 extends into a cavity 4 of the tool body 5, and this cavity has at its bottom a smaller diameter portion 6 which allows the precise location of the fiber end. A button 7 on an arm 8 of the tool is used to actuate the clamping element 9 in the connector.
This tool requires the fiber end to be cleaved prior to insertion into the connector and ferrule. If the fiber end face is damaged after cleaving, i.e., during insertion into the connector, then the cleaving operation must be repeated. An improper cleave can even cause the fiber to break inside the ferrule. Since this operation also requires that the fiber be cleaved at a specific distance from the end of the buffer coating, this coating may have to be stripped further. In this design, the fiber must further be secured to the collar (via clamping element 9) prior to securing the cable jacket with any strain relief crimp. If the fiber is not first clamped, then it may move backwards in the connector body due to forces exerted by the crimping ring on the buffer coating, and the fiber end face will consequently not be positioned at the bottom of smaller diameter portion 6. Conversely, however, this same phenomenon results in tensile stress in the fiber between the clamping element and the strain relief crimp. Such stress may cause the fiber to break, or still to be pulled back slightly in spite of the clamping element. Moreover, these conditions may occur during connector installation, or at an indefinite point in time during use.
If the cleave is poor quality, hackeled edges at the end of the fiber might not leave enough fiber protruding from the end of the ferrule to perform a proper polish. Compensating for this possibility by making the smaller diameter portion 6 deeper leaves a greater length of protruding fiber which is more easily broken by transverse forces generated during polishing. This tool thus requires a quality cleaver and a skilled technician, adding expense to the overall process. It would, therefore, be desirable to devise a tool which allows the precise positioning of the end of an optical fiber with respect to the ferrule end face, and allows cleaving of the fiber after it has been inserted into the connector and ferrule, and which additionally allows a strain relief crimp to be applied prior to securing the fiber in the ferrule, eliminating the possibility of tensile stresses in the fiber and end face location errors. It would be further advantageous if the tool eliminated the need for a quality cleaver.